The present invention relates to a sewing machine for trace stitching along the stitching line distant from the edge of the work fabric by a desired distance, and more specifically to a fabric edge trace stitching system in which the degree of tracing along the fabric edge is changeable.
Generally, such an electronically controlled zigzag sewing machine for trace stitching along the stitching line distant from the fabric edge by a desired distance is already in practical use.
For example, the Japanese Patent Publication (not examined) No. 61-257675 discloses a zigzag sewing machine for trace stitching comprising a needle swing mechanism driven with a needle swing control motor, a fabric edge detector installed on the needle bar supporting member of the needle swing mechanism which includes a light-emitting device for emitting infrared rays and a light-receiving device for receiving reflected infrared rays reflected at a reflecting surface provided on the throat plate, and a control means for controlling the lateral position of the fabric edge detector through the needle swing control motor so as to trace the fabric edge based on the trace width setting signal from a trace width setting volume and the detected voltage representing total amount of the reflected infrared rays. This sewing machine facilitates to form a seam along the stitching line distant from the fabric edge by a desired distance by controlling the fabric edge detector to trace the fabric edge.
Furthermore, the Japanese Patent Publication (not-examined) No. 63-277090 discloses the same kind of a sewing machine which comprises a timing pulse generator and a control means for storing and renewing the past newest four detected position signals output from the fabric edge detector in syhchronism with the timing pulse and for determining the average of above four detected position signals as the next needle position.
The fabricating process for fabricating utility goods made of the fabric includes various steps such as a step for cutting the work fabric, a step for forming the plain seam and a step for forming the stitch seam.
In case of the plain seam, it is useless to form a seam tracing precisely along the fabric edge because of frayed (loosen) portions or roughly cut portions on the fabric edge, and therefore it is preferrable to form a seam tracing smoothly and approximately along the fabric edge.
On the other hand, in case of the stitch seam, since the stitch seam is formed along the folded fabric edge in many cases, it is preferrable to form a seam tracing precisely along the folded fabric edge.
However, the sewing machine disclosed in the former patent publication is suitable for the stitch seam tracing precisely along the fabric edge, but this sewing machine is not suitable for the plain seam. In the sewing machine disclosed in the latter patent publication, since each stitching position is determined based on the average of the past four stitching positions, this sewing machine is suitable for the plain seam tracing smoothly and approximately along the fabric edge, but this sewing machine is not suitable for the stitch seam.